泡沫金属结构对流动沸腾换热特性的影响

随着航空航天领域的发展采用沸腾换热的高效换热技术越来越受到关注,泡沫金属具有比表面积大、导热系数高的优 点,可以强化流动沸腾换热的效果。本文在实验工况为孔密度10-40PPI,干度0.1-0.9,质流密度90-180kg/(m2·s),热流密度12.4-18.6kW/m2的条件下,研究了表面润湿性为未改性和疏水改性的泡沫金属管内制冷剂流动沸腾换热的情况。结果表 明:40PPI泡沫金属管比10PPI泡沫金属管的沸腾换热表面传热系数最多增大了96%;随着干度.质流密度和热流密度的增大,泡沫金属管内流动沸腾换热表面传热系数最多分别增大74%,95%以及48%;疏水改性增加了泡沫表面的成核点数,与未改性相 比可以使传热系数增大10%-30%。     

含油制冷剂在泡沫金属圆管内流动沸腾的换热特性

实验研究了填充泡沫金属的圆管内制冷剂与润滑油混合物流动沸腾换热特性。实验对象为两根分别填充5PPI、90%孔隙率与10PPI、90%孔隙率泡沫铜的圆管,以及相同管径的光管。实验工况为蒸发压力995kPa,质流密度为10~30 kg/(m2.s),热流密度为3.1~9.3kW/m2,入口干度0.175~0.775,油浓度为0~5%。实验结果表明:纯制冷剂工况下,泡沫金属的存在强化流动沸腾换热,换热系数最多提高185%;含油工况下,泡沫金属强化换热的效果弱化;相同工况下,更小的孔径可以提高流动沸腾换热系数,相比5PPI泡沫金属的实验数据,10PPI的泡沫金属可以使换热系数最多提高0.6倍。基于流型建立了填充泡沫金属的圆管内制冷剂与润滑油流动沸腾换热系数的预测模型,预测模型与98%的实验数据误差在±30%以内。     

金属泡沫在纳米流体池内沸腾换热特性研究

常压下,以去离子水或纳米流体为工质,对光滑平板和沸腾池内铺设金属泡沫,进行池内沸腾实验研究:分析了不同过热度下的热流密度和不同热流密度下池沸腾的传热系数;对沸腾汽泡在光滑平板和泡沫金属表面产生、融合和脱离进行了可视化的研究。实验发现:纳米流体工质会影响金属泡沫池内沸腾特性。     

肋类型对水平单管管外沸腾换热性能影响

本文选用近共沸制冷剂R4I0A,对相同尺寸的一根光管和两根双侧强化管进行了管外沸腾换热实验研究。对于光管管外沸腾换热,将实验结果分别结合Coper公式和Gaenflo公式得到的管内表面传热系数与经验公式计算值进行了对比,结果显示两者误差保持在15%以下,验证了实验结果的准确性。运用Wilsn图解法分别求得两根换热管管内换热强化倍率分别为1.85~2.05和2.02~2.25,通过不同方式改变热流量,综合对比1#换热管和2#换热管总传热系数与管两侧表面传热系数,结果 均显示由于强化管肋类型的不同, I#换热管管外表面结构更有利于汽化核心形成气泡,比2#换热管总传热系数高约10%,管外 表面传热系数高约20%~25%,更加符合强化水平单管管外池沸腾换热的要求。     

泡沫金属中池沸腾传热的研究进展

介绍了泡沫金属的结构特性,总结了泡沫金属中池沸腾的气泡生长速度、气泡直径和气泡生长现象等传热特点,以及泡沫金属的孔隙率、孔密度等参数对池沸腾传热的影响,并指出了泡沫金属中沸腾传热的研究方向。     

泡沫金属中池沸腾传热的研究进展

介绍了泡沫金属的结构特性，总结了泡沫金属中池沸腾的气泡生长速度、气泡直径和气泡生长现象等传热特点，以及泡沫金属的孔隙率、孔密度等参数对池沸腾传热的影响，并指出了泡沫金属中沸腾传热的研究方向。     

用于空间绿色发动机蓄换热的泡沫镍材料的性能研究

针对空间绿色单组元发动机热启动工况,搭建了蓄换热实验装置,研究了泡沫镍的厚度、孔密度、体密度等参数对其与流动介质瞬时换热能力的影响。研究表明,泡沫镍的瞬时换热能力随厚度的增加而增强;在孔密度较小时(20~70PPI),比表面积是影响泡沫镍的瞬时换热能力的关键因素,瞬时换热能力随孔密度和体密度的增加而增强;在孔密度较高时(100PPI),流阻成为影响泡沫镍的瞬时换热能力的主要因素,泡沫镍的瞬时换热能力大幅增强,但随体密度的增加变化不明显。搭建了强制对流条件下泡沫材料流阻实验装置,测量和比较了泡沫镍与催化剂的流阻,发现泡沫镍的流阻随孔密度和体密度的增加而增大,所有泡沫镍的流阻均小于催化剂的流阻。从实际应用角度看,应综合考虑蓄换热实验、点火实验结果和对泡沫金属的力学性能要求等多项因素来选择泡沫金属的参数。     

R717在小管径水平光管内流动沸腾换热及压降特性

氨制冷剂存在可燃性和毒性,因此减少其在制冷系统中的充注量极为重要。小管径换热管通常可以提供更高的表面传热系数,这可以作为提升换热器紧凑性同时减少系统中充注量的有效方法。本文搭建了氨制冷剂管内流动沸腾换热及压降测试实验装置,测试了氨制冷剂在4 mm水平光管内的流动沸腾换热及压降,并分析了干度、质量流速及热流密度对换热及压降特性的影响。结果表明:流动沸腾换热表面传热系数随着干度的增加而增大,同时质量流速和热流密度越高,流动沸腾换热表面传热系数越大。此外,氨制冷剂在管内的两相摩擦压降也随着干度的增加而增大,在固定干度下,质量流速的升高导致压降增大。     

基于碳纳米管的含油纳米制冷剂核态池沸腾换热特性

通过实验研究了基于碳纳米管(CNTs)的含油纳米制冷剂(即由制冷剂R113、润滑油VG68和碳纳米管组成的纳米流体)的核态池沸腾换热特性,分析了碳纳米管对含油制冷剂核态池沸腾换热的影响.实验中采用了外径为15～80nm、长度为1.5～10μm的四种碳纳米管.实验的饱和压力为101.3 kPa;热流密度为10～80 kW/m2;纳米油(碳纳米管和润滑油的混合物)的质量分数为0～5％;在纳米油中碳纳米管的质量分数为0～30％.实验结果表明:碳纳米管增强了含油制冷剂的池沸腾换热,在测试工况下换热系数最大可增加61％.当纳米油中碳纳米管浓度为20％不变,纳米油浓度由1％提高到5％时,不同尺寸的碳纳米管对换热系数的增加幅度由27％～59％降低至23％～55％;当纳米油的浓度为1％不变,纳米油中碳纳米管浓度由20％提高到30％时,不同尺寸的碳纳米管对换热系数的增加幅度由27％～59％升高到33％～61％.通过实验获得了基于碳纳米管的含油纳米制冷剂池沸腾换热关联式,关联式的预测值与96％的实验数据偏差在±10％以内.     

蒸发温度对强化换热管管外核态池沸腾换热性能的影响

对R134a在水平强化管(Φ25 mm)外核态池沸腾进行了实验研究。通过Wilson图解法求得管内换热准则关系式,通过改变蒸发温度(5.6℃,0℃,-2℃,-4℃,-6℃,-8℃)和热流密度(4~55 k W/m2),得到了管外沸腾换热系数随热流密度和蒸发温度变化的规律。实验表明,管外沸腾换热系数随着热流密度和蒸发温度的升高而增加。结合实验数据,提出了一个新的管外池沸腾换热关联式,该关联式与实验数据点的偏差显示,95%的数据点的相对误差在±20%以内。     

Insertion of triangulated surfaces into a meccano tetrahedral discretization by means of mesh refinement and optimization procedures

In this paper, we present a new method for inserting several triangulated surfaces into an existing tetrahedral mesh generated by the meccano method. The result is a conformal mesh where each inserted surface is approximated by a set of faces of the final tetrahedral mesh. First, the tetrahedral mesh is refined around the inserted surfaces to capture their geometric features. Second, each immersed surface is approximated by a set of faces from the tetrahedral mesh. Third, following a novel approach, the nodes of the approximated surfaces are mapped to the corresponding immersed surface. Fourth, we untangle and smooth the mesh by optimizing a regularized shape distortion measure for tetrahedral elements in which we move all the nodes of the mesh, restricting the movement of the edge and surface nodes along the corresponding entity they belong to. The refining process allows approximating the immersed surface for any initial meccano tetrahedral mesh. Moreover, the proposed projection method avoids computational expensive geometric projections. Finally, the applied simultaneous untangling and smoothing process delivers a high‐quality mesh and ensures that the immersed surfaces are interpolated. Several examples are presented to assess the properties of the proposed method.     

Certification Institutions Expected to Update and Transfer Information on Present Standards

Standards are the basis for production enterprises to organize production, ex-factory inspection, trade (delivery) and technical exchanges, product certification, quality arbitration and supervision.……     

The Research of Anti-Wear Properties of Organomolybdenum Compounds in the Engine Oils

A four-ball tester was used to evaluate the anti-wear performance of three kinds of organomolybdemun compounds in the engine oils, i. e., molybdenum dialkyldithiophosphate (MoDDP), molybdenum dialkyldithiocarbamate ( MoDTC), and sulphur and phosphorus freeorganomolybdeum (Molybdate). The results indicate that a low concentration of MoDDP doesn' t improve the anti-wear properties of the commercial engine oils, but a high concentration of MoDDP can obviously improve the anti-wear properties and the load-carrying capacity of the engine oils. MoDTC doesn' t improve the antiwear properties of the engine oils, but worsens the anti-wear properties of the oils. Signifi can timprove ment of frictional and wear characteristics is obtained with Molybdate added in the commercial engine oils and the formulated oils.     

Flow calorimeter for enthalpy increment measurements on condensed gases

A flow calorimeter for enthalpy increment measurements on condensed gases is presented. A better knowledge of the properties of the liquefied natural gas is needed, and therefore a liquid loop has been designed for our flow calorimeter. The fluid loop in the calorimeter is designed in order to avoid the two-phase region, since two phases would give compositional disturbances in the measurements. The avoidance of the two-phase region is made possible by increasing the pressure of the test fluid after the measurement section, then heating the fluid at super-critical pressure past the critical point. Finally, the fluid is throttled to the low-pressure gas state at the inlet condition of the compressor that circulates the fluid. To perform the pressure increase, a new cryogenic pump has been designed. To evaluate the new equipment, measurements were taken on liquid ethane over the temperature range 146–256 K at pressure between 0.9 and 5.1 MPa.     

Refrigerators Enter a New Era of Health Preservation Frestech initiates the establishment of China's first standard for household sterilization refrigerators

On November 30, 2007, the China Association for Standardization (CAS) held a press conference at Beijing Diaoyutai State Guest House. Leaders from the China Household Electric Appliance Research Institute, the China Household Electric Appliance Association, and the China Consumers' Association attended and made speeches.……     

Optimum-Simulation von Ernteprozessen

Zusammenfassung Bei der Gestaltung von Ernteprozessen — beispielsweise des Prozesses Mähdrusch, Körnertransport und -abnahme — als transportverbundene Fließarbeitsverfahren mit mindestens zwei verschiedenen Arbeitsmitteln gibt es einen großen Optimierungsspielraum. Solche Prozesse sind mehrstufige Bedienungsprozesse mit gemischter Anordnung der Bedienungseinrichtungen. Außerdem besitzen sie stark ausgeprägte räumliche Aspekte. Es wird vor allem gezeigt, welche Merkmale solcher Prozesse in Simulationsmodellen abgebildet sein müssen, welche Zielgrößen in Abhängigkeit von welchen Einflußgrößen unter Berücksichtigung welcher Prozeßbedingungen ermittelt werden sollten und wie der Bewertungsprozeß zur Ermittlung der gewünschten Informationen gestaltet werden muß.     

A study of centrifugal cast high boron high speed steel

In the present study a high‐boron high speed steel (HSS) roll material was designed. Many expensive alloy elements have been substituted by cheap boron alloy, and high‐boron high speed steel roll has been manufactured by centrifugal casting method. The microstructures, mechanical properties and wear resistance of centrifugal casting high‐boron high speed steel roll have been investigated by optical microscopy (OM), scanning electron microscopy (SEM), and X‐ray diffraction (XRD) analysis, hardness test, impact test and wear test. The results indicated that the solidification microstructures of high‐boron high speed steel roll consisted of M₂(B,C), (W,Mo)₂(B,C), M₃(B,C), M₂₃(B,C)₆ type borocarbides and martensite, a small amount of retained austenite. Borocarbides were continuously distributed over the grain boundary. After quenching from 1050 °C, local broken network appeared in partial borocarbides, and fine secondary borocarbide precipitated from the matrix. After tempering from 525 °C, the amount of precipitated borocarbide increased significantly. After heat treatment, the hardness of high‐boron high speed steel roll excelled 60 HRC, and its impact toughness excelled 8.0 J/cm². The single groove steel rolling amount of high‐boron high speed steel rolls increases by 500% than that of bainite cast iron roll, when the rolls are used in K₁ mill housing of bar mill.     

Certification Becomes Important for the I Quality; and Safety Supervision of the Chinese Liquor Sector

The end of 2007, over 200 unit products of more than 80 Chinese firms have passed the quality grade certification for liquor products. These products involve distilled spirits, beer, wine, yellow wine, fruit syrup wine and others, and cover over 80% of the national top-branded liquor products.……     

Deposition and Coating Properties on CVD Tungsten

Surface characterization and microstructure studies are performed on chemical vapor deposited (CVD) tungsten coating. There is about 2 μm thickness diffusion layer of tungsten in the molybdenum substrate. The thermal shock test shows tungsten coating has good adhesion with molybdenum substrate, but the elements of oxygen and carbon in the tungsten coating have the bad affection to the adhesion. The result of high-temperature diffusion experiment is the diffusion rate from molybdenum substrate to tungsten coating is faster.